1. Field of the Invention
The present invention relates to exhaust valve devices for a two-cycle engine, and more particularly to exhaust valves for two-cycle engines provided with a first exhaust valve for varying exhaust timing of an exhaust port, and a second exhaust valve positioned in an exhaust passage for varying a sectional area of the exhaust passage. The present invention particular relates to an exhaust valve device having a simplified drive mechanism.
2. Description of the Background Art
Japanese Unexamined Patent Publication Hei 5-125945 shows an exhaust valve device of a two-cycle engine provided with a first exhaust valve for varying the timing of the opening/closing of an exhaust port, and a second exhaust valve positioned in an exhaust passage for varying a sectional area of the exhaust passage. The exhaust valves are each arranged so as to be driven and controlled by rotation with a different drive shaft.
Further, since rotation angles of the first exhaust valve and the second exhaust valve are different from each other due to a difference between the opening and closing positions, a gear drive mechanism is provided in order to vary the rotation angles.
There are several drawbacks when a separate exclusive drive shaft and a drive mechanism are provided in an attempt to drive a first exhaust valve and a second exhaust valve as in the conventional embodiment described hereinabove. The conventional arrangements have increased numbers of parts, additional weight, and increased component costs. These conventional arrangements also create a reduction in the degree of freedom permitted in design layout.
The present invention overcomes the shortcomings associated with the conventional art and achieves other advantages not realized by the conventional art.
It is an object of the present invention to reduce the number of component parts required with traditional exhaust valve operation.
It is an object of the present invention to reduce manufacturing costs and to increase the designer""s options for system design layout.
It is an object of the present invention to reduce overall engine weight.
These and other aspects of the present invention are accomplished by an exhaust valve device for a two-cycle engine comprising a first exhaust valve for varying an exhaust timing of an exhaust port; a second exhaust valve for varying a sectional area of an exhaust passage; a common drive shaft rotated at a prescribed valve drive timing drivingly engaging said first exhaust valve and said second exhaust valve, wherein a second angular range of rotation of said second exhaust valve is larger than a first angular range of rotation of said first exhaust valve; and a linkage mechanism provided between said first exhaust valve and said second exhaust valve, said second exhaust valve integrally rotating with said first exhaust valve within the first angular range of rotation, and the second exhaust valve independently rotatable from said first exhaust valve when the second angular range of rotation exceeds said first angular range of rotation.
In the present invention, since a first exhaust valve and a second exhaust valve are mounted on a common drive shaft, a linkage mechanism for mutually linking operation of either valve can be provided. The first exhaust valve and the second exhaust valve are interlocked with each other up to a rotation limit of the first exhaust valve. However, only the second exhaust valve is rotated with an angle of rotation more than the first exhaust valve""s rotation limit when the drive shaft is rotated with a prescribed valve drive timing.
Accordingly, since the drive shaft of both the exhaust valves can be on a common drive shaft and a single drive mechanism or linkage mechanism is utilized, a decrease in the number of part items, in weight, and in cost can be achieved. Further, an increase in a degree of freedom of design layout can be realized.
Further, a coupling member moving in an axial direction of a drive shaft is provided, the first exhaust valve and a second exhaust valve coupled and interlocked with each other by the coupling member within a first angular range of rotation of the first exhaust valve. The second exhaust valve is separated from the first exhaust valve by moving the coupling member when second angular range of rotation exceeds a first rotation limit of the first exhaust valve. The second exhaust valve independently rotates in angular rotational ranges in excess of the first rotation limit.
These and other aspects of the present invention are accomplished by an exhaust valve assembly for an engine comprising an exhaust port; an exhaust passage arranged in a downstream position with respect to said exhaust port; a valve containing chamber formed between said exhaust port and said exhaust passage; a first exhaust valve for varying an exhaust timing by varying a height of the exhaust port; a second exhaust valve for varying a sectional area of the exhaust passage; a common drive shaft rotated at a prescribed valve drive timing drivingly engaging said first exhaust valve and said second exhaust valve, wherein a second angle of rotation of said second exhaust valve is larger than a first angle of rotation of said first exhaust valve; and a linkage mechanism provided between said first exhaust valve and said second exhaust valve, the second exhaust valve independently rotatable from said first exhaust valve when the second angle of rotation exceeds a first rotation limit of the first exhaust valve.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.